Various plastic devices used in medical applications require sterilization. Such devices include flexible tubing and small intravenous fluid bags for packaging drugs. Several methods of sterilization are currently available. These include steam, ethylene oxide and gamma radiation. Gamma radiation may be defined as electromagnetic radiation similar to x-rays except that gamma rays orginate in the nucleus of an atom whereas x-rays originate in the extra nuclear structure. Gamma rays usually have higher energies and shorter wavelengths than x-rays. Radiation normally causes polymers such as PVC and polypropylene to break down in chain length (loss of inherent viscosity) with corresponding loss of physical properties, discoloration, etc. Most of the medical tubing used today is sterilized by ethylene oxide but this method has a drawback in that there is a need to insure no residual ethylene oxide in the plastic material.
U.S. Pat. No. 3,091,600 discloses linear aromatic acid copolyesters modified with dimer glycols having 36 carbon atoms that are stable to sterilization by gamma radiation. This patent claims polyesters having melting points of at least 200.degree. C. The compositions disclosed in the present invention all melt at less than 200.degree. C.
U.S. Pat. No. 3,915,913 and U.S. Pat. No. 3,931,073 relate to polyesters of dimer acid modified with poly-(tetramethylene terephthalate) which can be blended with a vinyl aromatic polymer such as polystyrene or an aliphatic hydrocarbon. U.S. Pat. No. 4,216,129 involves molding compositions comprising a blend of poly(tetramethylene terephthalate) and poly(tetramethylene terephthalate) modified with dimer acid. The compositions disclosed in the present invention are copolyesters and do not involve blends of admixtures in any way.